Studies have been carried out in dogs with recently-induced complete atrioventricular block to determine the effects of drive on ventricular pacemaker activity. It was found that overdrive of the ventricles may induce the onset of ventricular rhythms instead of suppression. It was also shown that the rhythms elicited are also subject to overdrive suppression. It was then possible by selecting appropriate procedures to obtain pure overdrive suppression, pure overdrive excitation, or a graded mixture of the two. The conclusion of these studies should make it possible to attack the problem of arrhythmias resulting from ligation of the left anterior descending coronary artery on a sounder basis of understanding. Bibliographic references: The effect of high cervical cordotomy on portal vein plasma serotonin and 5-hydroxyindoleacetic acid levels in dogs with and without superior mesenteric artery occlusion. Newman, F.A., Strauss, R.D., Reznick, S.E., Bortolussi, M.E., Cummins, M.J., and Stuckey, J.H. Surgery 77:154, 1975.